The default GC has had some major performance improvements in .NET Core/5+. If you look up the performance improvement blog posts on MS dev blogs that come out

The default GC has had some major performance improvements in .NET Core/5+. If you look up the performance improvement blog posts on MS dev blogs that come out shortly before each new .NET release you can see some of the details. Definitely not the same wealth of alternative GCs like there are available for Java, but it performa significantly better than it did in. NET 4.x. Also there have been tons of overall improvements to decrease total heap allocations, see Span<T> for one of the biggest ones.